The present invention relates to a semiconductor injection laser, and, particularly to a high efficiency, self-pulsing semiconductor injection laser which can be simply pulsed with very short width pulses.
Semiconductor injection lasers, in general are bodies of a single crystalline semiconductor material which, when biased, emit light, either visible or infrared, through the recombination of pairs of oppositely charged carriers. Such devices generally include regions of opposite conductivity type forming a PN junction therebetween. When the junction is properly biased, charge carriers of one type are injected from one of the regions into the other where the predominant charge carriers are of the opposite type so as to achieve the light generating recombination.
To provide a semiconductor injection laser which is capable of efficient emission of stimulated radiation at room temperature, various structures have been devised which include an optically confining cavity between regions of opposite conductivity type in which the generation of radiation by the recombination of the charge carriers occurs. The cavity is generally a narrow region extending across the semiconductor body between the ends and side edges of the body. Optical confinement is usually achieved by making the regions of the body on each side of the cavity of a material having an index of refraction lower than that of the material of the cavity. At least one end edge of the body is made partially transmitting so as to form a Fabry-Perot cavity. Thus, the radiation generated in the optically confining cavity is emitted from the partially transmitting end edge of the body as a beam of coherent radiation. Some structures of semiconductor injection lasers having optically confining cavities are described in the articles "Close-Confinement Gallium Arsenide PN Junction Lasers with Reduced Optical Loss at Room Temperature," by H. Kressel et al, RCA REVIEW, Volume 30, No. 1, pages 106-113, March, 1969, "High-Order Transverse Cavity Modes in Heterojunction Diode Lasers" by J. Butler et al., APPLIED PHYSICS LETTERS, Volume 17, No. 9, Nov. 1, 1970, pages 403-406, and "An Efficient Large Optical Cavity Injection Laser" by H. F. Lockwood et al., APPLIED PHYSICS LETTERS, Volume 17, No. 12, Dec. 1, 1970, pages 499-502.
For certain types of uses, such as laser communications, it is desirable to operate the semiconductor injection laser with very short width pulses, e.g., pulse widths of 4 nanoseconds or less. However, to so operate previously known types of the semiconductor injection lasers requires expensive and complicated current drivers.
There has been developed a semiconductor light emitting diode which includes internal means for switching the diode off and on with the application of a small voltage. This type of diode is of a PNPN structure and is described in the article entitled, "Electroluminescent Shockley Diodes in GaAs and GaAs.sub.1.sub.-x P.sub.x " by C. J. Nuese et al., Journal of Electronic Materials, Vol. 2, pages 571-599, November, 1973, and U.S. Pat. No. 3,757,174 issued Sept. 4, 1973 to J. Shigemasu et al., entitled "Light Emitting-Four Layer Semiconductor Device." However, I have found that merely to provide such a PNPN light emitting diode with a laser cavity or to apply the concept of the PNPN light emitting diode to a semiconductor injection laser of the types described in the above cited articles does not necessarily result in an operative semiconductor injection laser.